This invention relates to a device for feeding cigarettes in bulk to the hopper of a packaging machine. In feed systems for cigarette packaging machines, it is known to utilise feed devices comprising a mobile wall feed channel arranged to continuously receive cigarettes in bulk from at least one cigarette production machine, a compartment arranged for connection to the inlet hopper of said packaging machine and to receive cigarettes from said feed channel, and at least one mobile wall store communicating with said compartment and controlled by means for measuring the quantity of cigarettes present therein.
In these known feed devices, said compartment is normally constituted by a substantially vertical fall channel, of which the upper end is connected to the outlet end of said feed channel and the lower end is connected to said hopper.
Normally, a substantially vertical side wall of the fall channel comprises apertures aligned one below the other and each constituting the inlet-outlet mouth of a respective said mobile wall store.
This latter is normally controlled by a respective pressure sensor disposed in a side wall of the fall channel in a position facing said inlet-outlet mouth. When in operation, the cigarettes are fed to the packaging machine hopper by moving transversely to themselves along the fall channel at a relatively high flow speed, and apply to the walls of the fall channel a pressure normally lying between a predetermined minimum value and a predetermined maximum value.
If for any reason the rate of absorption of the cigarettes by the packaging machine falls, the pressure inside the fall channel increases until it reaches and then exceeds said maximum value, with the result that said pressure sensors cause said stores to operate in the sense that their mobile walls move in such a manner as to receive the excess cigarettes which are not absorbed by the packaging machine.
In contrast, if the packaging machine operates normally and the cigarette production rate of the production machine decreases, the pressure inside the fall channel decreases to below said minimum value, so that said pressure sensors cause said stores to operate in the sense that their mobile walls move in order to feed into the fall channel a quantity of cigarettes sufficient to compensate for the reduction in the production rate of the production machine.
Generally, known feed devices as heretofore described operate correctly only when the flow speed of the cigarettes along the fall channel is relatively low. Instead, when a packaging machine of high production rate is used, for example a packaging machine capable of producing up to seven packets per second, the relatively high flow speed of the cigarettes along the fall channel hinders correct operation of the pressure sensors. This is because these latter are generally disposed in front of the mouths of the respective stores, i.e. at points in the fall channel at which the cigarette flow is particularly disturbed due to the fact that in each of these positions one of the walls of the fall channel is defined by the cigarettes at rest over the store mouth.
Because of contact with the cigarettes moving rapidly along the fall channel, these stationary cigarettes tend not only to rotate about their own axis in the manner of rollers of a roller guide, thus expelling their tobacco, but also to emerge from the mouth of the relative store to add to the cigarettes in movement, so creating small pressure waves. If the pressure sensors are sufficiently sensitive (as is necessary for feed systems for fast packaging machines) these pressure waves can cause sudden undesirable operation of the stores, which can be particularly damaging.